Unified block vector prediction for intra picture block compensation

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. An apparatus for video decoding includes processing circuitry that decodes prediction information for a current block in a current coded picture. The prediction information indicates an intra block copy (IBC) prediction mode used for the current block, an index to select a block vector predictor candidate from a block vector predictor candidate list for the current block, and whether a non-zero residue exists for the current block. The processing circuitry constructs the block vector predictor candidate list for the current block in a same sequence of candidates, no matter whether the no-zero residue exists for the current block. The processing circuitry selects a block vector predictor candidate from the constructed block vector predictor candidate list based on the index indicated in the prediction information and reconstructs the current block according to the selected block vector predictor candidate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. § 120 from U.S. application Ser. No. 16/531,827 filedAug. 5, 2019, and claims the benefit of priority from U.S. ApplicationNo. 62/816,051 filed Mar. 8, 2019, the entire contents of each of whichare incorporated herein by reference.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or maybe predicted itself.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 1B shows a schematic (105) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

A current block can include samples that have been found by the encoderduring the motion search process to be predictable from a previous blockof the same size that has been spatially shifted. Instead of coding thatMV directly, the MV can be derived from metadata associated with one ormore reference pictures, for example from the most recent (in decodingorder) reference picture, using the MV associated with either one offive surrounding samples, denoted A0, A1, and B0, B1, B2. In H.265, theMV prediction can use predictors from the same reference picture thatthe neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry.

The processing circuitry is configured to decode prediction informationfor a current block in a current coded picture that is a part of a codedvideo sequence. The prediction information indicates an intra block copy(IBC) prediction mode used for the current block, an index to select ablock vector predictor candidate from a block vector predictor candidatelist for the current block, and whether a non-zero residue exists forthe current block. The processing circuitry constructs the block vectorpredictor candidate list for the current block in response to theindication that the non-zero residue does not exist for the currentblock. The block vector predictor candidate list has a first number ofblock vector predictor candidates and is constructed based on a sequenceof candidates. Otherwise, the processing circuitry constructs the blockvector predictor candidate list for the current block in response to theindication that the non-zero residue exists for the current block. Theblock vector predictor candidate list has a second number of blockvector predictor candidates and is constructed based on the samesequence of candidates. The processing circuitry further selects a blockvector predictor candidate from the constructed block vector predictorcandidate list based on the index indicated in the predictioninformation. Finally, the processing circuitry reconstructs the currentblock according to the selected block vector predictor candidate.

According to an aspect of the disclosure, the processing circuitryfurther determines whether a first block vector of a first spatialneighboring block of a plurality of spatial neighboring blocks of thecurrent block is available. The processing circuitry inserts the firstblock vector into the block vector predictor candidate list in responseto the determination that the first block vector of the first spatialneighboring block of the plurality of spatial neighboring blocks of thecurrent block is available. The processing circuitry determines whethera second block vector of a second spatial neighboring block of theplurality of spatial neighboring blocks of the current block isavailable and whether the second block vector of the second spatialneighboring block is the same as the first block vector of the firstspatial neighboring block. The processing circuitry inserts the secondblock vector into the block vector predictor candidate list in responseto the determination that the second block vector of the second spatialneighboring block of the plurality of spatial neighboring blocks of thecurrent block is available and that the second block vector of thesecond spatial neighboring block is not the same as the first blockvector of the first spatial neighboring block.

In an embodiment, the first spatial neighboring block of the currentblock is adjacent to a lower-left corner of the current block and abottom side of the first spatial neighboring block is aligned to abottom side of the current block, and the second spatial neighboringblock of the current block is adjacent to an upper-right corner of thecurrent block and a right side of the second spatial neighboring blockis aligned to a right side of the current block.

In another embodiment, the first spatial neighboring block of thecurrent block is adjacent to the lower-left corner of the current blockand a top side of the first spatial neighboring block is aligned to thebottom side of the current block, and the second spatial neighboringblock of the current block is adjacent to the upper-right corner of thecurrent block and a left side of the second spatial neighboring block isaligned to the right side of the current block.

In another embodiment, the first spatial neighboring block of thecurrent block is adjacent to a left side of the current block and thesecond spatial neighboring block of the current block is adjacent to atop side of the current block.

In an embodiment, when a total number of the block vectors of theplurality of spatial neighboring blocks included in the block vectorpredictor candidate list is less than a maximum allowed number that isbased on whether the non-zero residue exists for the current block, theprocessing circuitry selects a third block vector of a previously codedblock from a plurality of block vectors of previously coded blocks. Theprocessing circuitry determines whether the selected third block vectoris different from the plurality of spatial neighboring blocks includedin the block vector predictor candidate list. The processing circuitryinserts the selected third block vector into the block vector predictorcandidate list in response to the determination that the selected thirdblock vector is different from the plurality of spatial neighboringblocks included in the block vector predictor candidate list.

In an embodiment, when a total number of the block vectors of theplurality of spatial neighboring blocks and the previously coded blocksincluded in the block vector predictor candidate list is less than themaximum allowed number and is above one, the processing circuitryselects a plurality of block vector predictor candidates from the blockvector predictor candidate list. The processing circuitry averages theselected plurality of block vector predictor candidates to form at leastone averaged block vector. The processing circuitry inserts the at leastone averaged block vector into the block vector predictor candidatelist.

In an embodiment, when a total number of the block vectors of theplurality of spatial neighboring blocks, the block vectors of thepreviously coded blocks, and the at least one average block vectorincluded in the block vector predictor candidate list is less than themaximum allowed number, the processing circuitry inserts a default blockvector into the block vector predictor candidate list.

In an embodiment, the default block vector is (0, 0).

In an embodiment, the selected block vector predictor candidate is notrounded when the non-zero residue exists for the current block.

In an embodiment, when one of the block vector predictor candidatesincluded in the block vector predictor candidate list is invalid, theprocessing circuitry performs a pruning process or clipping process tothe one of the block vector predictor candidates.

In an embodiment, the one of the block vector predictor candidates isdetermined to be invalid when a reference block predicted by the one ofthe block vector predictor candidates is out of an allowed search rangefor intra block copy (IBC) prediction mode.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 shows an example of the intra block copy (IBC) prediction mode,according to an embodiment of the disclosure.

FIGS. 9A-9D show an example of an updating process for a search range ofthe IBC prediction mode, according to an embodiment of the disclosure.

FIG. 10 shows an example of a valid block vector that follows certainconstraints, according to an embodiment of the disclosure.

FIG. 11 shows an example of spatial neighboring-based block vectors,according to an embodiment of the disclosure.

FIG. 12 shows a flow chart outlining an exemplary process according toan embodiment of the disclosure.

FIG. 13 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick, and the like.

A streaming system may include a capture subsystem (313) that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values that canbe input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation that the intra prediction unit (452) has generated to theoutput sample information as provided by the scaler/inverse transformunit (451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415) andthe parser (420) may not be fully implemented in the local decoder(533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quad-tree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

In general, block based compensation based on a different picture may bereferred to as motion compensation or inter prediction blockcompensation. However, block compensation may be done from a previouslyreconstructed area within a same picture. Such block compensation may bereferred to as intra picture block compensation, current picturereferencing (CPR), or intra block copy (IBC).

Aspects of the disclosure provide techniques for block basedcompensation within a same picture (e.g., IBC prediction mode).

According to aspects of the disclosure, in the IBC prediction mode, adisplacement vector that indicates an offset between a current block anda reference block within the same picture is referred to as a blockvector (BV). It is noted that the reference block is alreadyreconstructed prior to the current block. In addition, for parallelprocessing, a reference area that is at a tile/slice boundary orwave-front ladder shape boundary may be excluded from being used as anavailable reference block. Due to these constraints, a block vector maybe different from a motion vector that can be at any value (positive ornegative, at either x or y direction) in motion compensation of theinter prediction mode.

The coding of a block vector in the IBC prediction mode can be eitherexplicit or implicit. In the explicit mode, a block vector differencebetween a block vector and a predictor of the block vector is signaled.A way of coding a block vector in the explicit mode of the IBCprediction mode may be similar to a way of coding a motion vector inadvanced motion vector prediction (AMVP) mode of the inter predictionmode. In the implicit mode, a block vector is recovered from a predictorof the block vector without using a block vector difference, in asimilar way as a motion vector prediction in merge mode of the interprediction mode. In addition, the resolution of a block vector may berestricted to integer positions in one embodiment but may be allowed topoint to fractional positions in another embodiment.

The use of the IBC prediction mode at the block level can be signaledusing, for example, a block level flag (referred to as an IBC flag) or areference index. When using the IBC flag, the current block may not becoded in implicit mode. When using the reference index, the currentdecoded picture can be treated as a reference picture that is put in alast position of a reference picture list. This reference picture mayalso be managed together with other temporal reference pictures in adecoded picture buffer (DPB).

FIG. 8 shows an example of the intra block copy (IBC) prediction mode,according to an embodiment of the disclosure. In the example of FIG. 8,a current picture (800) is being reconstructed and includes areconstructed area (801) (gray area) and a to-be-decoded area (802)(white area). The blocks in the reconstructed area (801) are alreadydecoded and the blocks in the to-be-reconstructed area (802) are eitherbeing decoded or to-be-decoded. A current block (804) is in theto-be-reconstructed area (802) and being decoded. The current block(804) can be decoded from a reference block (805) that is in thereconstructed area (801). The decoding of the current block (804) isbased on a block vector (803) that is an offset between the currentblock (804) and the reference block (805).

According to aspects of the disclosure, a reference picture (e.g.,reference block (805)) used to derive a block vector (e.g., block vector(803)) for a current block (e.g., current block (804)) is within asearch range of the IBC prediction mode.

According to some embodiments, a search range of the IBC prediction modeis constrained to be within a current CTU where a current block resides.In an example, a memory to store reference samples for the search rangeof the IBC prediction mode is 1 CTU size (e.g. 128×128 samples). If 1CTU size (128×128 samples) includes four regions with each region having64×64 samples, the memory may store such four regions, in which oneregion may be currently reconstructed 64×64 samples and the other threeregions with each region having 64×64 samples may be reference samples.

According to some embodiments, a search range of the IBC prediction modecan be extended to some parts of a left CTU of the current CTU whilekeeping the memory to store the search range unchanged (e.g., 1 CTUsize), so that the search range may not be constrained to be within thecurrent CTU. It is noted that the search range may depend on a positionof a current block in the current CTU. That is, the search range may beupdated according to the position of the current block in the currentCTU.

FIGS. 9A-9D show an example of an updating process for a search range ofthe IBC prediction mode, according to an embodiment of the disclosure.As described above, the effective search range is extended to some partsof a left CTU (910) of a current CTU (900).

During this updating process, the stored reference samples from the leftCTU are updated with the reconstructed samples from the current CTU. InFIGS. 9A-9D, gray color regions indicate already reconstructed regions,white color regions indicate to-be-reconstructed regions, and regionswith vertical stripes and text “Curr” indicate current coding/decodingregions where current blocks reside. In addition, in each figure, theleft four regions (911)-(914) belong to the left CTU (910) and the rightfour regions (901)-(904) belong to the current CTU (900).

It is noted that all of four regions (911)-(914) of the left CTU (910)are already reconstructed. Thus, the memory initially stores all ofthese four regions of reference samples from the left CTU (910), andthen updates a region of reference samples from the left CTU (910) witha same relative region of currently reconstructed samples from thecurrent CTU (900).

For example, in FIG. 9A, a current region (901) in the current CTU (900)is under reconstruction, and a co-located region in the left CTU (910)of the current region (901) is an already reconstructed region (911).The co-located region (911) is in a region of the left CTU (910) withthe same relative region as the current block (901) in the current CTU(900). Thus, the memory region that stores reference samples of theco-located region (911) is updated to store the reconstructed samples ofthe current region (901), and an “X” is marked in the co-located region(911) in FIG. 9A to indicate that the reference samples of theco-located region (911) are no longer stored in the memory.

Similarly, in FIG. 9B, a current region (902) in the current CTU (900)is under reconstruction, and a co-located region in the left CTU (910)of the current region (902) is a region (912). The co-located region(912) is in a region of the left CTU (910) with the same relative regionas the current region (902) in the current CTU (900). Thus, the memoryregion that stores reference samples of the co-located region (912) isupdated to store the reconstructed samples of the current region (902),and an “X” is marked in the co-located region (912) in FIG. 9B toindicate that the reference samples of the co-located region (912) areno longer stored in the memory.

In FIG. 9C, a current region (903) in the current CTU (900) is underreconstruction, and a co-located region in the left CTU (910) of thecurrent region (903) is a region (913). The co-located region (913) isin a region of the left CTU (910) with the same relative region as thecurrent region (903) in the current CTU (900). Thus, the memory regionthat stores reference samples of the co-located region (913) is updatedto store the reconstructed samples of the current region (903), and an“X” is marked in the co-located region (913) in FIG. 9C to indicate thatthe reference samples of the co-located region (913) are no longerstored in the memory.

In FIG. 9D, a current region (904) in the current CTU (900) is underreconstruction, and a co-located region in the left CTU (910) of thecurrent region (904) is a region (914). The co-located region (914) isin a region of the left CTU (910) with the same relative region as thecurrent region (904) in the current CTU (900). Thus, the memory regionthat stores reference samples of the co-located region (914) is updatedto store the reconstructed samples of the current region (904), and an“X” is marked in the co-located region (914) in FIG. 9D to indicate thatthe reference samples of the co-located region (914) are no longerstored in the memory.

According to aspects of the disclosure, a valid block vector that isderived within a search range of the IBC prediction mode may follow someconstraints to meet bitstream conformance conditions.

FIG. 10 shows an example of a valid block vector (1020) that followscertain constraints, according to an embodiment of the disclosure. Inthe FIG. 10 example, a current CTB (1000) is a luma CTB including fourluma regions (1006)-(1009). When a derivation process for referenceblock availability is invoked, a position (xCurr, yCurr) of a top-leftsample of a current block (1003) in the current CTB (1000) is set to be(xCb, yCb), and the valid luma block vector (1020) may follow certainconstraints. The valid luma block vector (1020) points from the currentblock (1003) to a reference block (1015) in a left CTB (1010) of thecurrent CTB (1000).

According to some embodiments, a first constraint is that a referenceblock for the current block is already reconstructed. In an example, fora rectangle reference block, a reference block is determined to bealready reconstructed when both a top-left sample and a bottom-rightsample of the reference block are already reconstructed. Specifically,for a luma block vector mvL with 1/16 pel resolution, when a position(xCb+(mvL[0]>>4), yCb+(mvL[1]>>4)) of the top-left sample of thereference block is input, a TRUE is output, indicating the top-leftsample of the reference block is already reconstructed. It is noted thatmvL[0] and mvL[1] are x component and y component of the two dimensionalluma block vector mvL. Similarly, when a position(xCb+(mvL[0]>>4)+cbWidth−1, yCb+(mvL[1]>>4)+cbHeight−1) of thebottom-right sample of the reference block is input, a TRUE is output,indicating the bottom-right sample of the reference block is alreadyreconstructed. It is noted that the parameters cbWidth and cbHeightrepresent a width and a height of the reference block. Accordingly, whenboth positions (xCb+(mvL[0]>>4), yCb+(mvL[1]>>4)) and(xCb+(mvL[0]>>4)+cbWidth−1, yCb+(mvL[1]>>4)+cbHeight−1) are input, aTRUE is output, indicating both of the top-left sample and thebottom-right sample of the reference block, as well as the referenceblock itself, are already reconstructed, and thus, the block vector isvalid, as shown in FIG. 10. However, if the reference block is notalready reconstructed, the luma block vector mvL may be invalid.

According to some embodiments, a second constraint is that the referenceblock does not overlap with the current block. Under the constraint thatthe reference block is already constructed, the reference block can beeither to the left of the current block or to the top of the currentblock in order to avoid overlapping with the current block. In anexample, for a luma block vector mvL with 1/16 pel resolution, at leastone of the two values (mvL[0]>>4)+cbWidth and (mvL[1]>>4)+cbHeight isless than or equal to 0. Specifically, the value (mvL[0]>>4)+cbWidth isless than or equal to 0, indicating that the reference block is to theleft of the current block and does not overlap with the current block.Similarly, the value (mvL[1]>>4)+cbHeight is less than or equal to 0,indicating the reference block is to the top of the current block anddoes not overlap with the current block. Accordingly, if both values(mvL[0]>>4)+cbWidth and (mvL[1]>>4)+cbHeight are more than 0, thereference block overlaps with the current block so that the luma blockvector mvL of the current block may be invalid.

According to some embodiments, a third constraint is that a CTB wherethe reference block resides is either a left neighboring CTB of acurrent CTB or the current CTB itself. In an example, for a luma blockvector mvL with 1/16 pel resolution, equations (1)-(4) are satisfied tomeet this constraint:

(yCb+(mvL[1]>>4))>>Ctb Log 2SizeY=yCb>>Ctb Log 2SizeY  (1)

(yCb+(mvL[1]>>4)+cbHeight−1)>>Ctb Log 2SizeY=yCb>>Ctb Log 2SizeY  (2)

(xCb+(mvL[0]>>4))>>Ctb Log 2SizeY≥(xCb>>Ctb Log 2SizeY)−1  (3)

(xCb+(mvL[0]>>4)+cbWidth−1)>>Ctb Log 2SizeY≤(xCb>>Ctb Log 2SizeY)  (4)

It is noted that the parameter Ctb Log 2SizeY represents a CTB width inlog 2 form. For example, if the CTB width is 128 samples, the parameterCtb Log 2SizeY is 7. Specifically, equations (1) and (2) indicate thatthe CTB where the reference block resides is in a same CTB row as thecurrent CTB, and equations (3) and (4) indicate that the CTB where thereference block resides is either in a left CTB column of the currentCTB or a same CTB column as the current CTB. Accordingly, the equations(1)-(4) are satisfied, indicating that the reference block resides ineither the left neighboring CTB, such as the left CTB (1010) in the FIG.10 example, of the current CTB (1000) or the current CTB (1000) itself.However, if the reference block does not reside in either of the leftneighboring CTB of the current CTB or the current CTB itself, the lumablock vector mvL is invalid.

According to some embodiments, a fourth constrain is that when thereference block resides in the left neighboring CTB of the current CTB,a co-located region of the reference block in the current CTB has notbeen reconstructed. The co-located region of the reference block in thecurrent CTB is a region in the current CTB with the same relative regionas the reference block in the left neighboring CTB. Referring back toFIG. 10, the reference block (1015) resides in the region (1012) of theleft neighboring CTB (1010), therefore, the co-located region of thereference block (1015) in the current CTB (1000), i.e., the region(1017), has not been reconstructed. In an example, for a luma blockvector mvL with 1/16 pel resolution, when the equation (5) is satisfied,

(xCb+(mvL[0]>>4))>>Ctb Log 2SizeY=(xCb>>Ctb Log 2SizeY)−1 (5) and aposition of the co-located region in the current CTB(((xCb+(mvL[0]>>4)+CtbSizeY)>>(Ctb Log 2SizeY−1))<<(Ctb Log 2SizeY−1),((yCb+(mvL[1]>>4))>>(Ctb Log 2SizeY−1))<<(Ctb Log 2SizeY−1)) is input, aFALSE is output. It is noted that the parameter CtbSizeY represents theCTB width. Specifically, the equation (5) indicates that the referenceblock is in the left neighboring CTB of the current CTB.

Still referring back to FIG. 10, when one of the coding blocks(1002)-(1003) is a current block, a reference block cannot be in theregion (1011), and thus, a search range for the one of the coding blocks(1002)-(1003) excludes the region (1011), which is marked “X” similar toFIG. 9A. The reasons are as follow: if the reference block is in theregion (1011), then a co-located region for the reference block is theregion (1006), however, at least some samples in the coding block (1001)have been reconstructed, thus the fourth constraint is violated. On theother hand, for a coding block to be reconstructed first in a currentregion, such as the coding block (1001) in the region (1006) of thecurrent CTB (1000), the fourth constraint does not prevent a referenceblock to be in the region (1011) because the co-located region (1006)for the reference block has not been reconstructed yet, for example,such that the reference samples of the region (1011) are not overwrittenor deleted.

According to aspects of the disclosure, the IBC prediction mode isconsidered as a separate mode or a third mode in addition to the intraprediction mode and inter prediction mode. That is, the IBC predictionmode is different from either the intra prediction mode or the interprediction mode. By doing this, the block vector prediction in implicitmode (similar to the merge mode of the inter prediction mode) andexplicit mode (similar to the AMVP mode of the inter prediction mode)are separated from regular inter prediction mode.

A separate predictor candidate list is defined for the implicit mode ofthe IBC prediction mode. The separate predictor candidate list of theimplicit mode of the IBC prediction mode differs from a merge candidatelist in the merge mode of the inter prediction mode in that all theentries in the predictor candidate list are block vectors. The candidatederivation process of the separate predictor candidate list may be basedon the candidate derivation process of a merge candidate list. As anexample, the 5 spatial neighboring locations in the merge mode of theinter prediction mode in HEVC or VVC standards can be accessed for theIBC prediction mode to derive its own predictor candidate list for theimplicit mode. In addition, another separate predictor candidate listmay be defined for the explicit mode of the IBC prediction mode, whereall the entries in the list are also block vectors. The candidatederivation process of the separate predictor candidate for the explicitmode list may be based on that of a predictor candidate list in the AMVPmode of the inter prediction mode.

Accordingly, as a separate mode from the inter prediction mode, the IBCprediction mode can have a simplified and unified block vectorderivation process for both implicit mode and explicit mode.

According to aspects of the disclosure, a block vector predictorcandidate list of the IBC prediction mode includes a plurality of blockvector predictor candidates and each of the plurality of block vectorpredictor candidates can be from one of the following block vectors: ablock vector of spatial neighboring-based block vectors, a block vectorof history-based block vectors, an averaged block vector, and a blockvector of default block vectors.

FIG. 11 shows an example of spatial neighboring-based block vectors,according to an embodiment of the disclosure. A current block (1100) has5 spatial neighboring blocks (1101)-(1105) in the bottom-left,top-right, and top-left positions.

In one embodiment, an order of forming a block vector predictorcandidate list of the IBC prediction mode from the 5 spatial neighboringblocks is: A0 (1101)->B0 (1102)->B1 (1103)->A1 (1104)->B2 (1105).

In one embodiment, only A0 and B0 from the spatial neighboring-basedblock vectors may be contained in a block vector predictor candidatelist. When both A0 and B0 are available but equal to each other, onlyone may be included in the block vector predictor candidate list.

In one embodiment, only A1 and B1 from the spatial neighboring-basedblock vectors may be contained in a block vector predictor candidatelist. When both A1 and B1 are available but equal to each other, onlyone may be included in the block vector predictor candidate list.

In one embodiment, only Ax and By from the spatial neighboring-basedblock vectors may be contained in a block vector predictor candidatelist, where Ax and By represents one of the left neighbors and one ofthe top neighbors, respectively.

According to some embodiments, history-based block vector predictor(HBVP) candidates are included in a block vector predictor candidatelist. In an example, a HBVP candidate may be included in a block vectorpredictor candidate list after the spatial neighboring-based blockvectors. The HBVP candidate is derived based on a previously coded blockand is stored in a HBVP table. The HBVP table with multiple HBVPcandidates is maintained during the encoding/decoding process. The HBVPtable can be reset (emptied) when a new CTU row is encountered. Wheneverthere is a non-sub-block IBC CU, the associated block vector is added toa last entry of the HBVP table as a new HBVP candidate.

According to some embodiments, the HBVP table size S is set to be 6,indicating up to 6 HBVP candidates may be added to the table. Wheninserting a new HBVP candidate to the HBVP table, a constrainedfirst-in-first-out (FIFO) rule is utilized where a redundancy check isfirst applied to the HBVP table in order to find whether there is anidentical or similar HBVP candidate in the HBVP table. In an example,when an identical or similar HBVP candidate is found in the HBVP table,the identical or similar HMVP is removed from the HBVP table such thatall the HBVP candidates afterwards can be moved forward.

It is noted that the HBVP table size can be varied in some embodiments.That is, the size S can be less or more than 6 in some embodiments. Whenthe size is more than 6, in some embodiments, no pruning is used whenincluding a new HBVP candidate into the HBVP table.

According to some embodiments, when constructing a block vectorpredictor candidate list, the latest several HBVP candidates in the HBVPtable are checked in order and included in the candidate list after thespatial neighboring-based candidates. Redundancy check is applied on theHBVP candidates to the spatial neighboring-based candidates. To reducethe number of redundancy check operations, a number of HBPV candidatesused for constructing a block vector predictor candidate list is set as(N<=4) ? M: (8−N), where N indicates a number of existing candidates inthe candidate list and M indicates a number of available HBVP candidatesin the HBVP table. Once the total number of available block vectorpredictor candidates reaches a maximally allowed number minus 1, theblock vector predictor candidate list construction process from HBVP isterminated.

According to some embodiments, an averaged block vector may be includedinto a block vector predictor candidate list. The averaged block vectorcan be derived by selecting a plurality of predictor candidates from thecandidate list and then averaging the selected predictor candidates.

In one example, a first candidate and a second candidate are averaged toform a new candidate in the list.

In another example, the first three candidates are averaged in pairs toform a set of three new candidates. An order of the three new candidatesderived from the first three existing candidates may be (1st, 2nd),(1st, 3rd) and (2nd, 3rd), where 1st, 2nd, and 3rd correspond to thefirst three existing candidates in the list, respectively.

In another example, the first four candidates are averaged in pairs toform a set of six new candidates. An order of the six new candidatesderived from the first four existing candidates may be (1st, 2nd), (1st,3rd), (2nd, 3rd), (1st, 4th), (2nd, 4th), (3rd, 4th), where 1st, 2nd,3rd, and 4th correspond to the first four existing candidates in thelist, respectively.

According to some embodiments, default block vectors can be included ina block vector predictor candidate list. The default block vectors canbe predefined.

In one embodiment, constant based block vectors may be used. Someexample default block vectors include, but are not limited to (0, 0),(−8, 0), (0, −8), (−4, 0), (0, −4), (−8, −8), and (−4, −4). These blockvectors, in whole or in part, may be arranged in the above order to beincluded in a block vector predictor candidate list, or may be in otherorders.

In one embodiment, block size related block vectors may be used. Someexample default block vectors include, but are not limited to (−2w, 0),(0, −2h), (−w, 0), (0, −h), (−2w, −2h), and (−w, −h), where w and hrepresent a width and a height of a current block, respectively. Theseblock vectors, in whole or in part, may be arranged in the above orderto be included in a block vector predictor candidate list, or may be inother orders.

In one embodiment, maximum block size related block vectors may be used.Some example default block vectors include, but are not limited to(−2w_max, 0), (0, −2h_max), (−w_max, 0), (0, −h_max), (−2w_max,−2h_max), and (−w_max, −h_max), where w_max and h_max represent amaximum allowed width and a maximum allowed height of a current block,respectively. These block vectors, in whole or in part, may be arrangedin the above order to be included in a block vector predictor candidatelist, or may be in other orders.

In one embodiment, minimum block size related block vectors may be used.Some example default block vectors include, but are not limited to(−2w_min, 0), (0, −2h_min), (−w_min, 0), (0, −h_min), (−2w_min,−2h_min), and (−w_min, −h_min), where w_min and h_min represent aminimum allowed width and a minimum allowed height of a current block,respectively. These block vectors, in whole or in part, may be arrangedin the above order to be included in a block vector predictor candidatelist, or may be in other orders.

In one embodiment, an order of candidates in a block vector predictorcandidate list is spatial neighboring-based block vectors->history-basedblock vectors->averaged block vectors->default block vectors.

In one embodiment, an order of candidates in a block vector predictorcandidate list is spatial neighboring-based block vectors->history-basedblock vectors->default block vectors.

According to aspects of the disclosure, a unified block vector predictorcandidate list can be used in both the implicit mode and the explicitmode of the IBC prediction mode. However, the candidate list may beapplied to only one of the implicit mode and the explicit mode of theIBC prediction mode. In one embodiment, when a candidate derived fromthis unified list is selected to be applied to the explicit mode, arounding of a selected block vector predictor candidate towards aselected block vector resolution may be disabled. That is, the selectedblock vector predictor candidate is at its original resolution, evenwhen a resolution of a block vector difference is at a differentresolution.

According to aspects of the disclosure, a block vector predictorcandidate list may be subject to a pruning or a clipping process. Thatis, if a block vector predictor in the list is considered as an invalidpredictor for a current block, for example, a reference block of thecurrent block in the IBC prediction mode will be out of an allowedsearch range if the invalid predictor is directly used as a final blockvector, then an additional operation is performed.

In one embodiment, in a pruning process, all of invalid candidates in acandidate list are removed from the list such that subsequent validcandidates can be moved up in the list.

In one embodiment, in a pruning process, one or more invalid candidatesin a candidate list are removed from the list. Examples of invalidcandidates include, but are not limited to candidates that do not followa constraint that a reference block does not overlap with a currentblock and candidates that do not follow a constraint that a CTB where areference block of a current block resides is either a left neighboringCTB of a current CTB or the current CTB itself.

In one embodiment, in a clipping process, invalid candidates are clippedsuch that each of the clipped candidates points to positions inside avalid search range of the IBC prediction mode. Such a clipping processcan be done by modifying a horizontal, a vertical, or both components ofa block vector predictor in a way that after the modification, the blockvector predictor points to a border of the valid search range of the IBCprediction mode.

FIG. 12 shows a flow chart outlining an exemplary process (1200)according to an embodiment of the disclosure. The process (1200) can beused in the reconstruction of a block coded in an IBC prediction mode,so as to generate a prediction block for a block under reconstruction.In various embodiments, the process (1200) are executed by processingcircuitry, such as the processing circuitry in the terminal devices(210), (220), (230) and (240), the processing circuitry that performsfunctions of the video encoder (303), the processing circuitry thatperforms functions of the video decoder (310), the processing circuitrythat performs functions of the video decoder (410), the processingcircuitry that performs functions of the intra prediction module (452),the processing circuitry that performs functions of the video encoder(503), the processing circuitry that performs functions of the predictor(535), the processing circuitry that performs functions of the intraencoder (622), the processing circuitry that performs functions of theintra decoder (772), and the like. In some embodiments, the process(1200) is implemented in software instructions, thus when the processingcircuitry executes the software instructions, the processing circuitryperforms the process (1200).

The process (1200) may generally start at step (S1210), where theprocess (1200) decodes prediction information for a current block in acurrent coded picture that is a part of a coded video sequence. Theprediction information indicates an intra block copy (IBC) predictionmode is used for the current block. The prediction information can alsoindicate an index to select a block vector predictor candidate from ablock vector predictor candidate list for the current block, and whethera non-zero residue exists for the current block. After decoding theprediction information, the process (1200) proceeds to step (S1220).

At step (S1220), the process (1200) determines whether a non-zeroresidue exists for the current block based on the predictioninformation. If the process (1200) determines that the non-zero residuedoes not exist for the current block, then the process (1200) proceedsto step (S1230). Otherwise, the process (1200) proceeds to step (S1240).

At step (S1230), the process (1200) constructs the block vectorpredictor candidate list for the current block in response to theindication that the non-zero residue does not exist for the currentblock. The block vector predictor candidate list has a first number ofblock vector predictor candidates and is constructed based on a sequenceof candidates.

At step (S1240), the process (1200) constructs the block vectorpredictor candidate list for the current block in response to theindication that the non-zero residue exists for the current block. Theblock vector predictor candidate list has a second number of blockvector predictor candidates and is constructed based on the samesequence of candidates that is processed in step (S1230).

In an embodiment, the process (1200) determines whether a first blockvector of a first spatial neighboring block of a plurality of spatialneighboring blocks of the current block is available. In response to thedetermination that the first block vector of the first spatialneighboring block of the plurality of spatial neighboring blocks of thecurrent block is available, the process (1200) adds the first blockvector into the block vector predictor candidate list. Otherwise, theprocess (1200) determines whether a second block vector of a secondspatial neighboring block of the plurality of spatial neighboring blocksof the current block is available and in some embodiments, whether thesecond block vector of the second spatial neighboring block is the sameas or similar to the first block vector of the first spatial neighboringblock. In response to the determination that the second block vector ofthe second spatial neighboring block of the plurality of spatialneighboring blocks of the current block is available and in someembodiments, that the second block vector of the second spatialneighboring block is not the same as the first block vector of the firstspatial neighboring block, the processing circuitry adds the secondblock vector into the block vector predictor candidate list.

In an embodiment, the first spatial neighboring block of the currentblock is adjacent to a lower-left corner of the current block and abottom side of the first spatial neighboring block is aligned to abottom side of the current block, and the second spatial neighboringblock of the current block is adjacent to an upper-right corner of thecurrent block and a right side of the second spatial neighboring blockis aligned to a right side of the current block.

In one embodiment, the first spatial neighboring block of the currentblock is adjacent to the lower-left corner of the current block and atop side of the first spatial neighboring block is aligned to the bottomside of the current block, and the second spatial neighboring block ofthe current block is adjacent to the upper-right corner of the currentblock and a left side of the second spatial neighboring block is alignedto the right side of the current block.

In one embodiment, the first spatial neighboring block of the currentblock is adjacent to a left side of the current block and the secondspatial neighboring block of the current block is adjacent to a top sideof the current block.

In one embodiment, when a total number of the block vectors of theplurality of spatial neighboring blocks included in the block vectorpredictor candidate list is less than a maximum allowed number that isbased on, for example, whether the non-zero residue exists for thecurrent block, the process (1200) selects a third block vector of apreviously coded block from a plurality of block vectors of previouslycoded blocks. The process (1200) may determine whether the selectedthird block vector is different from the plurality of spatialneighboring blocks included in the block vector predictor candidatelist. In response to the determination that the selected third blockvector is different from the plurality of spatial neighboring blocksincluded in the block vector predictor candidate list, the process(1200) adds the selected third block vector into the block vectorpredictor candidate list.

In one embodiment, when a total number of the block vectors of theplurality of spatial neighboring blocks and the previously coded blocksincluded in the block vector predictor candidate list is less than themaximum allowed number and is above one, the process (1200) selects aplurality of block vector predictor candidates from the block vectorpredictor candidate list. The process (1200) averages the selectedplurality of block vector predictor candidates to form at least oneaveraged block vector. The process (1200) adds the at least one averagedblock vector into the block vector predictor candidate list.

In one embodiment, when a total number of the block vectors of theplurality of spatial neighboring blocks, the block vectors of thepreviously coded blocks, and the at least one average block vectorincluded in the block vector predictor candidate list is less than themaximum allowed number, the process (1200) adds one or more defaultblock vectors into the block vector predictor candidate list.

After constructing the block vector predictor candidate list for thecurrent block, the process (1200) proceeds to step (S1250).

At step (S1250), the process (1200) selects a block vector predictorcandidate from the constructed block vector predictor candidate list,for example, based on an index indicated in the prediction information.The index may be signaled explicitly or implicitly.

After selecting the block vector predictor candidate, the process (1200)proceeds to step (S1260).

At step (S1260), the process (1200) reconstructs the current blockaccording to the selected block vector predictor candidate.

After reconstructing the current block, the process (1200) terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 13 shows a computersystem (1300) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 13 for computer system (1300) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1300).

Computer system (1300) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1301), mouse (1302), trackpad (1303), touchscreen (1310), data-glove (not shown), joystick (1305), microphone(1306), scanner (1307), camera (1308).

Computer system (1300) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1310), data-glove (not shown), or joystick (1305), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1309), headphones(not depicted)), visual output devices (such as screens (1310) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1300) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1320) with CD/DVD or the like media (1321), thumb-drive (1322),removable hard drive or solid state drive (1323), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1300) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1349) (such as, for example USB ports of thecomputer system (1300)); others are commonly integrated into the core ofthe computer system (1300) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1300) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1340) of thecomputer system (1300).

The core (1340) can include one or more Central Processing Units (CPU)(1341), Graphics Processing Units (GPU) (1342), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1343), hardware accelerators for certain tasks (1344), and so forth.These devices, along with Read-only memory (ROM) (1345), Random-accessmemory (1346), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1347), may be connectedthrough a system bus (1348). In some computer systems, the system bus(1348) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1348),or through a peripheral bus (1349). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1341), GPUs (1342), FPGAs (1343), and accelerators (1344) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1345) or RAM (1346). Transitional data can be also be stored in RAM(1346), whereas permanent data can be stored for example, in theinternal mass storage (1347). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1341), GPU (1342), massstorage (1347), ROM (1345), RAM (1346), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1300), and specifically the core (1340) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1340) that are of non-transitorynature, such as core-internal mass storage (1347) or ROM (1345). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1340). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1340) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1346) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1344)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

APPENDIX A: ACRONYMS AMVP: Advanced Motion Vector Prediction ASIC:Application-Specific Integrated Circuit BMS: Benchmark Set BV: BlockVector CANBus: Controller Area Network Bus CD: Compact Disc CPR: CurrentPicture Referencing CPUs: Central Processing Units CRT: Cathode Ray TubeCTBs: Coding Tree Blocks CTUs: Coding Tree Units CU: Coding Unit DPB:Decoder Picture Buffer DVD: Digital Video Disc FPGA: Field ProgrammableGate Areas GOPs: Groups of Pictures GPUs: Graphics Processing Units

GSM: Global System for Mobile communications

HEVC: High Efficiency Video Coding HRD: Hypothetical Reference DecoderIBC: Intra Block Copy IC: Integrated Circuit JEM: Joint ExplorationModel LAN: Local Area Network LCD: Liquid-Crystal Display LTE: Long-TermEvolution MV: Motion Vector OLED: Organic Light-Emitting Diode PBs:Prediction Blocks PCI: Peripheral Component Interconnect PLD:Programmable Logic Device PUs: Prediction Units RAM: Random AccessMemory ROM: Read-Only Memory SCC: Screen Content Coding SEI:Supplementary Enhancement Information SNR: Signal Noise Ratio SSD:Solid-state Drive TUs: Transform Units USB: Universal Serial Bus VUI:Video Usability Information VVC: Versatile Video Coding

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information for a current block in acurrent coded picture that is a part of a coded video sequence, theprediction information indicating an intra block copy (IBC) predictionmode used for the current block, and an index to select a block vectorpredictor candidate from a block vector predictor candidate list for thecurrent block; determining whether coding of the current block in theIBC prediction mode is performed in an explicit mode or an implicit modebased on whether a difference exists between a block vector and acorresponding block vector predictor, constructing the block vectorpredictor candidate list for the current block based on a sequence ofcandidates, the block vector predictor candidate list having a firstnumber of block vector predictor candidates in the implicit mode, andhaving a second number of block vector predictor candidates in theexplicit mode; selecting the block vector predictor candidate from theconstructed block vector predictor candidate list based on the indexindicated in the prediction information; and reconstructing the currentblock according to the selected block vector predictor candidate.
 2. Themethod of claim 1, further comprising: determining whether a first blockvector of a first spatial neighboring block of a plurality of spatialneighboring blocks of the current block is available; inserting thefirst block vector into the block vector predictor candidate list inresponse to the determination that the first block vector of the firstspatial neighboring block of the plurality of spatial neighboring blocksof the current block is available; determining whether a second blockvector of a second spatial neighboring block of the plurality of spatialneighboring blocks of the current block is available and whether thesecond block vector of the second spatial neighboring block is the sameas the first block vector of the first spatial neighboring block; andinserting the second block vector into the block vector predictorcandidate list in response to the determination that the second blockvector of the second spatial neighboring block of the plurality ofspatial neighboring blocks of the current block is available and thatthe second block vector of the second spatial neighboring block is notthe same as the first block vector of the first spatial neighboringblock.
 3. The method of claim 2, wherein the first spatial neighboringblock of the current block is adjacent to a lower-left corner of thecurrent block and a bottom side of the first spatial neighboring blockis aligned to a bottom side of the current block, and the second spatialneighboring block of the current block is adjacent to an upper-rightcorner of the current block and a right side of the second spatialneighboring block is aligned to a right side of the current block. 4.The method of claim 2, wherein the first spatial neighboring block ofthe current block is adjacent to the lower-left corner of the currentblock and a top side of the first spatial neighboring block is alignedto the bottom side of the current block, and the second spatialneighboring block of the current block is adjacent to the upper-rightcorner of the current block and a left side of the second spatialneighboring block is aligned to the right side of the current block. 5.The method of claim 2, wherein the first spatial neighboring block ofthe current block is adjacent to a left side of the current block andthe second spatial neighboring block of the current block is adjacent toa top side of the current block.
 6. The method of claim 2, furthercomprising: when a total number of the block vectors of the plurality ofspatial neighboring blocks included in the block vector predictorcandidate list is less than a maximum allowed number that is based onwhether the difference does exist between the block vector and thecorresponding block vector predictor for the current block; selecting athird block vector of a previously coded block from a plurality of blockvectors of previously coded blocks; determining whether the selectedthird block vector is different from the plurality of spatialneighboring blocks included in the block vector predictor candidatelist; and inserting the selected third block vector into the blockvector predictor candidate list in response to the determination thatthe selected third block vector is different from the plurality ofspatial neighboring blocks included in the block vector predictorcandidate list.
 7. The method of claim 6, further comprising: when atotal number of the block vectors of the plurality of spatialneighboring blocks and the previously coded blocks included in the blockvector predictor candidate list is less than the maximum allowed numberand is above one; selecting a plurality of block vector predictorcandidates from the block vector predictor candidate list; averaging theselected plurality of block vector predictor candidates to form at leastone averaged block vector; and inserting the at least one averaged blockvector into the block vector predictor candidate list.
 8. The method ofclaim 7, further comprising: when a total number of the block vectors ofthe plurality of spatial neighboring blocks, the block vectors of thepreviously coded blocks, and the at least one average block vectorincluded in the block vector predictor candidate list is less than themaximum allowed number, inserting a default block vector into the blockvector predictor candidate list.
 9. The method of claim 8, wherein thedefault block vector is (0, 0).
 10. The method of claim 1, wherein theselected block vector predictor candidate is not rounded when thedifference does exist between the block vector and the correspondingblock vector predictor for the current block.
 11. The method of claim 1,further comprising: when one of the block vector predictor candidatesincluded in the block vector predictor candidate list is invalid,performing a pruning process or clipping process to the one of the blockvector predictor candidates.
 12. The method of claim 11, wherein the oneof the block vector predictor candidates is determined to be invalidwhen a reference block predicted by the one of the block vectorpredictor candidates is out of an allowed search range for intra blockcopy (IBC) prediction mode.
 13. An apparatus, comprising a processingcircuitry configured to: decode prediction information for a currentblock in a current coded picture that is a part of a coded videosequence, the prediction information indicating an intra block copy(IBC) prediction mode used for the current block, and an index to selecta block vector predictor candidate from a block vector predictorcandidate list for the current block; determine whether coding of thecurrent block in the IBC prediction mode is performed in an explicitmode or an implicit mode based on whether a difference exists between ablock vector and a corresponding block vector; construct the blockvector predictor candidate list for the current block based on asequence of candidates, the block vector predictor candidate list havinga first number of block vector predictor candidates in the implicitmode, and having a second number of block vector predictor candidates inthe explicit mode; select the block vector predictor candidate from theconstructed block vector predictor candidate list based on the indexindicated in the prediction information; and reconstruct the currentblock according to the selected block vector predictor candidate. 14.The apparatus of claim 13, wherein the processing circuitry is furtherconfigured to: determine whether a first block vector of a first spatialneighboring block of a plurality of spatial neighboring blocks of thecurrent block is available; insert the first block vector into the blockvector predictor candidate list in response to the determination thatthe first block vector of the first spatial neighboring block of theplurality of spatial neighboring blocks of the current block isavailable; determine whether a second block vector of a second spatialneighboring block of the plurality of spatial neighboring blocks of thecurrent block is available and whether the second block vector of thesecond spatial neighboring block is the same as the first block vectorof the first spatial neighboring block; and insert the second blockvector into the block vector predictor candidate list in response to thedetermination that the second block vector of the second spatialneighboring block of the plurality of spatial neighboring blocks of thecurrent block is available and that the second block vector of thesecond spatial neighboring block is not the same as the first blockvector of the first spatial neighboring block.
 15. The apparatus ofclaim 14, wherein the first spatial neighboring block of the currentblock is adjacent to a lower-left corner of the current block and abottom side of the first spatial neighboring block is aligned to abottom side of the current block, and the second spatial neighboringblock of the current block is adjacent to an upper-right corner of thecurrent block and a right side of the second spatial neighboring blockis aligned to a right side of the current block.
 16. The apparatus ofclaim 14, wherein the first spatial neighboring block of the currentblock is adjacent to the lower-left corner of the current block and atop side of the first spatial neighboring block is aligned to the bottomside of the current block, and the second spatial neighboring block ofthe current block is adjacent to the upper-right corner of the currentblock and a left side of the second spatial neighboring block is alignedto the right side of the current block.
 17. The apparatus of claim 14,wherein the first spatial neighboring block of the current block isadjacent to a left side of the current block and the second spatialneighboring block of the current block is adjacent to a top side of thecurrent block.
 18. The apparatus of claim 14, wherein the processingcircuitry is further configured to: when a total number of the blockvectors of the plurality of spatial neighboring blocks included in theblock vector predictor candidate list is less than a maximum allowednumber that is based on whether the difference does exist between theblock vector and the corresponding block vector predictor for thecurrent block; select a third block vector of a previously coded blockfrom a plurality of block vectors of previously coded blocks; determinewhether the selected third block vector is different from the pluralityof spatial neighboring blocks included in the block vector predictorcandidate list; and insert the selected third block vector into theblock vector predictor candidate list in response to the determinationthat the selected third block vector is different from the plurality ofspatial neighboring blocks included in the block vector predictorcandidate list.
 19. The apparatus of claim 18, wherein the processingcircuitry is further configured to: when a total number of the blockvectors of the plurality of spatial neighboring blocks and thepreviously coded blocks included in the block vector predictor candidatelist is less than the maximum allowed number and is above one; select aplurality of block vector predictor candidates from the block vectorpredictor candidate list; average the selected plurality of block vectorpredictor candidates to form at least one averaged block vector; andinsert the at least one averaged block vector into the block vectorpredictor candidate list.
 20. A non-transitory computer-readable storagemedium storing a program that when executed by a decoder, causes thedecoder to perform a method comprising: decoding prediction informationfor a current block in a current coded picture that is a part of a codedvideo sequence, the prediction information indicating an intra blockcopy (IBC) prediction mode used for the current block, and an index toselect a block vector predictor candidate from a block vector predictorcandidate list for the current block; determining whether coding of thecurrent block in the IBC prediction mode is performed in an explicitmode or an implicit mode based on whether a difference exists between ablock vector and a corresponding block vector predictor, constructingthe block vector predictor candidate list for the current block based ona sequence of candidates, the block vector predictor candidate listhaving a first number of block vector predictor candidates in theimplicit mode, and having a second number of block vector predictorcandidates in the explicit mode; selecting the block vector predictorcandidate from the constructed block vector predictor candidate listbased on the index indicated in the prediction information; andreconstructing the current block according to the selected block vectorpredictor candidate.